The invention relates to a cleaning apparatus. More specifically, the invention is directed to an apparatus for cleaning the basket section of an air preheater, using a high energy wash stream.
Utility companies install air preheaters on steam generators to recover the sensible heat from the flue gas. In a conventional regenerative preheater, such as a Ljungstrom, the rotating baskets provide a continuous two-step process for preheating the combustion air. As the baskets rotate through the flue gas duct, hot flue gas flows through the corrugated baskets and heats the metal. As the baskets rotate into the air duct, cold combustion air is heated by contact with the hot metal. Air preheater seals separate the flue gas from the combustion air. During the heat transfer step, if the flue gas is cooled below its dew point, a condensate, which contains corrosive acidic materials, can form on the metal basket surfaces. Within a short time the deposits can cause a heat transfer problem in the preheater.
The heat transfer problem is particularly troublesome when coal is used as fuel for the boiler. The hot flue gas from burning coal carries slag, fly-ash, and other solid materials into the corrugated metal baskets. The larger particles become wedged between the plates in the baskets and cause a partial restriction of the air and gas flow through the preheater. In turn, the partial restriction accelerates deposition of the fly ash on the wet metal surfaces and rapidly causes a substantial pressure drop across the preheater. For example, at times the fly ash deposits can severly restrict passage of combustion air through the preheater, so that the boiler cannot operate at full load.
Prior methods for cleaning the preheater baskets have included steam blow, air blow, fire hose wash, system spray wash, and several other washing techniques. None of these procedures have been entirely satisfactory, particularly in trying to clean preheaters installed on boilers which burn coal with a high ash content. Prior to the invention of the present apparatus, the only alternative has been to periodically replace the preheater baskets, at considerable expense and downtime.